1. Field of the Invention
The present invention relates to subscriber-power-supply-control devices and subscriber-line circuits which are used along with a subscriber switch board for handling voice calls as well as internet calls.
2. Description of the Related Art
FIG. 1 is a block diagram showing a system configuration in which personal computers ;are accommodated via a digital-subscriber-switch board where the digital-subscriber-switch board generally deals with voice calls. The subscriber-switch board mainly includes a switch unit 1 and a central-control device 4, and accommodates conventional analog telephones TEL and modems of personal computers PC via subscriber-line circuits 2. Further, the subscriber-switch board accommodates modems belonging to computer-communication-service providers such as internet providers via a digital trunk 3. A power-supply device 7 is used for supplying power to the subscriber-switch board, and is also used for supplying power to subscriber-line circuits 2 and thence to the analog telephones.
In subscriber-switch boards handling voice calls, it is necessary to supply power to analog telephones. A direct current supplied to each analog telephone is used for detecting a start and an end of a call, and, also, is used for a voice/electric-current conversion in the telephone device. A typical level of power supply during a call is about 2 W (per each telephone) on average. In the case of an office-switch board servicing to more than ten thousand subscribers, for example, a total amount of supplied power reaches an enormous level, so that the power-supply device 7 needs to have a large capacity accordingly. Such a power-supply device 7 becomes an undesirably expensive. In general, the power-supply capacity of the power-supply device 7 is determined based on the power consumption of the subscriber-switch board as well as the power supply to the analog telephones, wherein the power-supply capacity relating to the power supply to the analog telephones is determined based on the number of subscribers simultaneously engaging in calls.
When personal computers PC are connected to the subscriber-switch board, modems are used as intermediaries for the connection. In this case, the subscriber-line circuits 2 supply power to modems, and the supplied current is used for detecting a start and an end of a call made by a personal computer PC. Since the personal computers PC receive AC power for their own operation from utility power supply, the current supplied from the subscriber-line circuit 2 is used for no purpose other than that of detecting a start and an end of a call.
A recent progress in use of personal-computer communications and the internet has resulted in a rapid increase in the number of data-communication calls, which are different from conventional voice calls in some aspects. Data-communication calls relating to the internet are referred to as internet calls. The internet call is generally characterized as being a lengthy call, which is held for a long time period to engage in an incessant communication. When the number of internet calls is increased, the amount of power supply is increased by a significant margin. In the case of a subscriber-switch board servicing to twenty-thausand subscribers, for example, the power-supply capacity of the power-supply device 7 is [150 A/xe2x88x9248 V] when most of the calls are expected to be voice calls. If a projection is given that the number of simultaneous calls will double because of an increase in the number of internet calls, the power-supply capacity of the power-supply device 7 needs to be [300 A/xe2x88x9248 V].
As the power-supply capacity of the power-supply device is increased in accordance with an increase in demand for the power supply, a price of the power-supply device will be increased, and so will be a cost of consumed power which is incurred as everyday expenses. As a result, a price of the switching system in its entirety as well as an operating cost thereof will be increased.
Accordingly, there is a need for preventing a power-supply capacity from being increased even when there is an increase in the number of non-conventional calls such as internet calls having different characteristics from those of conventional voice calls.
Accordingly, it is a general object of the present invention to satisfy the need described above.
It is another and more specific object of the present invention to prevent a power-supply capacity from being increased even when there is an increase in the number of non-conventional calls such as internet calls having different characteristics from those of conventional voice calls.
In order to achieve the above objects according to the present invention, a device for controlling power supply to subscribers in a digital subscriber-switch board includes subscriber-line circuits which supply power to the subscribers, and a carrier-detection unit which is connected to a communication path to detect a carrier signal of a modem once the communication path is established between a caller and a receiver, the caller being one of the subscribers, wherein one of the subscriber-line circuits corresponding to the one of the subscribers is controlled to suspend power supply to the one of the subscribers when the carrier-detection unit detects the carrier signal on the communication path.
In the device described above, the power supply from the subscriber-line circuit to the subscriber is suspended if a call made by the subscriber is a data-communication call. Therefore, a reduction can be made to the amount of power supply to the subscribers.
According to one aspect of the present invention, the device as described above is such that the carrier-detection unit continues to monitor the carrier signal on the communication path after the suspension of the power supply, and the one of the subscriber-line circuits is controlled to resume power supply to the one of the subscribers when the carrier-detection unit detects a termination of the carrier signal, the resumed power supply being used for monitoring an end of a call between the caller and the receiver.
In the device described above, the power supply to the subscriber is resumed after the termination of the carrier signal is detected during a data-communication call. Therefore, the resumed power supply can be used for detecting an end of the call just as in the case of a conventional voice call.
According to another aspect of the present invention, the device described above further includes a signal-termination-detection unit which checks whether a signal power is present in the communication path after the suspension of the power supply, wherein the one of the subscriber-line circuits is controlled to resume power supply to the one of the subscribers when the signal-termination-detection unit finds no signal power, the resumed power supply being used for monitoring an end of a call between the caller and the receiver.
In the device described above, the power supply to the subscriber is resumed if no signal power is detected during a data-communication call. Therefore, the resumed power supply can be used for detecting an end of the call just as in the case of a conventional voice call. Further, the signal-termination-detection unit has a sole function thereof in detecting a signal power, so that only a simple configuration is necessary for implementing the signal-termination-detection unit at a low cost.
According to another aspect of the present invention, the device described above further includes a central-control unit which is informed of a presence of the carrier signal by the carrier-detection unit, and controls the one of the subscriber-line circuits to suspend power supply to the corresponding one of the subscribers.
According to another aspect of the present invention, the device described above further includes a central-control unit which is informed of absence of the carrier signal by the carrier-detection unit, and controls the one of the subscriber-line circuits to resume power supply to the corresponding one of the subscribers.
According to another aspect of:the present invention, the device described above further includes a central-control unit which is informed of absence of the signal power by the signal-termination-detection unit, and controls the one of the subscriber-line circuits to resume power supply to the corresponding one of the subscribers.
According to another aspect of the present invention, the device described above is such that the communication path to which the carrier-detection unit is connected is a communication path on a receiver side.
In the device described above, a push-button signal transmitted from the subscribers is not confused, and does not bring about a false detection of a carrier signal.
According to another aspect of the present invention, the device described above is such that the carrier-detection unit includes a carrier-signal-detection unit which checks whether a signal is present within a range of carrier frequencies, an outside-band-signal-detection unit which checks whether a signal is present outside the range of carrier frequencies, and a check unit which detects a presence of the carrier signal when the carrier-signal-detection unit detects a presence of a signal within the range of carrier frequencies and the outside-band-signal-detection unit finds no signal outside the range of carrier frequencies, wherein the communication path to which the carrier-detection unit is connected is a communication path on a caller side.
In the device described above, even if a push-button signal containing some frequencies inside the range of carrier frequencies is transmitted from the caller side, such a signal can be distinguished from carrier signals, thereby avoiding a false detection of a carrier signal by confusing the push-button signal.
According to another aspect of the present invention, the device described above is such that the one of the subscriber-line circuits nullifies an on-hook-detection function thereof for at least a period during which the power supply is suspended.
In the device described above, even if the subscriber-line circuit generates a false on-hook-detection signal because of noises or the like during the suspension of power supply, such an on-hook-detection signal is ignored.
According to another aspect of the present invention, the device described above is such that the one of the subscriber-line circuits nullifies an on-hook-detection function thereof for a predetermined time period following a revival of the power supply.
In the device described above, even if the subscriber-line circuit generates a false on-hook-detection signal because of noises or the like during the predetermined period following the revival of power supply, such an on-hook-detection signal is ignored.
In order to achieve the objects previously described also according to the present invention, a subscriber-line circuit used in a digital subscriber-switch board and supplying power to a subscriber includes a carrier-detection unit which looks for a carrier signal of a modem on a communication path once the communication path is established through the subscriber-line circuit between a caller and a receiver, the caller being the subscriber, wherein the power supply to the subscriber is suspended when the carrier-detection unit detects the carrier signal on the communication path.
In the subscriber-line circuit described above, the power supply from the subscriber-line circuit to the subscriber is suspended if a call made by the subscriber is a data-communication call. Therefore, a reduction can be made to the amount of power supply to the subscribers.
According to one aspect of the present invention, the subscriber-line circuit as described above is such that the carrier-detection unit monitors the carrier signal on the communication path after the suspension of the power supply, and the power supply is resumed when the carrier-detection unit detects a termination of the carrier signal, the resumed power supply being used for monitoring an end of a call between the caller and the receiver.
In the device described above, the power supply to the subscriber is resumed after the termination of the carrier signal is detected during a data-communication call. Therefore, the resumed power supply can be used for detecting an end of the call just as in the case of a conventional voice call.
According to another aspect of the present invention, the subscriber-line circuit described above is such that the carrier-detection unit comprises a digital signal processor.
Functions of the subscriber-line circuits are implemented by using a digital signal processor in an increasing number of devices. In light of this, use of a digital signal processor for implementing the carrier-detection unit can achieve the configuration of the present invention solely based on an extension of software without expanding a hardware configuration, thereby preventing an undesirable increase in costs.
According to another aspect of the present invention, the subscriber-line circuit described above is such that the carrier-detection unit includes a carrier-signal-detection unit which checks whether a signal is present within a range of carrier frequencies, an outside-band-signal-detection unit which checks whether a signal is present outside the range of carrier frequencies, and a check unit which detects a presence of the carrier signal when the carrier-signal-detection unit detects a presence of a signal within the range of carrier frequencies and the outside-band-signal-detection unit finds no signal outside the range of carrier frequencies.
In the subscriber-line circuit described above, even if a push-button signal containing some frequencies inside the range of carrier frequencies is transmitted from the caller side, such a signal can be distinguished from carrier signals, thereby avoiding a false detection of a carrier signal by confusing the push-button signal.
According to another aspect of the present invention, the subscriber-line circuit described above is such that an on-hook-detection function thereof is nullified for at least a period during which the power supply is suspended.
In the subscriber-line circuit described above, even if the subscriber-line circuit generates a false on-hook-detection signal because of noises or the like during the suspension of power supply, such an on-hook-detection signal is ignored.
According to another aspect of the present invention, the subscriber-line circuit described above is such that an on-hook-detection function thereof is nullified for a predetermined time period following a revival of the power supply.
In the subscriber-line circuit described above, even if the subscriber-line circuit generates a false on-hook-detection signal because of noises or the like during the predetermined period following the revival of power supply, such an on-hook-detection signal is ignored.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.